Over 650,000 spine surgeries are performed annually in the United States, with the majority being decompressive laminectomies for spinal stenosis. Spinal stenosis is a narrowing of the spinal canal housing the spinal cord, which is generally caused by arthritis of articulating bones of the vertebral column and/or bulging of the intervertebral discs. Eighty percent of the population report having back pain, with over 400,000 patients per year diagnosed with spinal stenosis. The majority age group is 65 or older. The diagnosis of spinal stenosis and, therefore, need for treatment is likely to escalate rapidly when U.S. census data is applied. For example, the U.S. population of individuals over 65 represented 12.4% (about 35 million) in 2000 and is projected to represent 19.6% (million) by the year 2030.
The most common treatment for spinal stenosis involves a midline approach with a decompressive laminectomy to address the stenosis. Although highly effective in relieving the clauditory symptomotology, there is growing evidence and concern over the need for reoperation to address reoccurrence of symptoms related to progression of spondylolisthesis, or slippage, at the site of decompression. Slippage rates post-surgery have been reported as high as 20% in “no preop slip” patients and from 40% to 100% in “preop slip present” patients. The reoperation rate for each of these groups varies and is dependent on many factors. Reported reoperation rates average around 18% for the “no preop slip” group and upward of 30% for the “preop slip present” group.
The concern for further slippage and need for reoperation has fostered a treatment method involving the use of dynamic or motion sparing devices placed without a fusion to give some amount of “stiffness” to prevent further slippage and yet allow for some motion, avoid excessive loading of adjacent segments, and hopefully avoid adjacent segment disease. Such devices have been successful in limiting the progression of slip in stable spine constructs. However, there are recent reports of instrumentation failures and the need for revision surgery. Thus, the uses of dynamic systems are not always clinically successful and may defeat the attempt to limit reoperations. Furthermore, it is reported that adjacent segment disease continues similar to patients with rigid fusions. Furthermore, the need to utilize pedicle screw technology and approaches with such dynamic systems makes the muscle trauma morbidity comparable to undergoing a fusion surgery with screws and/or rods. Thus, alternative instrumentation is being explored by surgeons and engineers alike.